Color mapping data are data accompanying pictures or video signal and providing information to help mapping the colors of these pictures or video signal into another color space or color volume. A color volume is specified by color primaries and reference white and further by a dynamic range (i.e. min/max luminance peaks). Examples of such a color volumes are RGB BT.2020 with D65 reference white and with min luminance peak equal to 0 nit (or cd/m2) and max luminance peak equal to 4000 nits. RGB BT.2020 with D65 reference white and with min luminance peak equal to 0 nit (or cd/m2) and max luminance peak equal to 100 nits is another example of such a color volume. The document JCTVC R1013_v6 defines (sections D.2.27 and D.3.27) an SEI message “Mastering Display Color Volume SEI” specifying such a color volume.
The color mapping data defined in section D.3.32 of the document JCTVC R1013_v6 are example of such color mapping data. In this document, the color mapping data are indicated in a SEI message (SEI is the English acronym of “Supplemental Enhancement Information”). A color mapping function may be defined from several fields of the SEI message. The color mapping data may be created to enable to color map a version of video signal created for Blu-Ray into a version of the same video signal for DVD.
The color mapping data are usually determined in a studio or authoring facilities, i.e. on the production side, from RGB 4:4:4 or YUV 4:2:0 video signals. The color mapping data are not necessarily created at the same time as encoding the video signal. In fact, encoding the video signal and creating the color mapping data may be achieved by different operators. Consequently, when transmitting the color mapping data and the encoded video signal to a receiver, the receiver (specifically a decoder) is going to decode the color mapping data and the video signal without any knowledge of the conditions (e.g. information of the color space) of creation of the color data with respect to the conditions of encoding of the video signal. In these conditions, applying the color mapping data on the decoded video signal may degrade the color mapped decoded video signal.